@Ionus,
Ionus wrote: Does anyone know what a prosecutor is doing on an investigation board ?
A prosecutor is leading the investigation - here, in Germany, as well as in many other countries. (All investigations are being led by the public prosecution service, the prosectution ("Staatsanwaltschaft") is the so-called "Herrin des Verfahrens". [Police is an 'aiding organisation', "Hilfsorgan der Staatsanwaltschaft".]
The German prosecution office of Düsseldorf has taken over the investigation for/in Germany.
Ionus wrote:Before a decision is reached by a neutral investigation ?
Any "neutral investigation" e.g. by 'flight inspectors' etc is done to help the prosecution.